This invention generally relates to nanoparticle chargers.
Aerosol particles occur in the air we inhale and may have an adverse effect on the human health. In addition, inhalers for medical applications produce different kinds of aerosol particles of different sizes, including nanoparticles where not only the presence but also the size distribution of the aerosol particles is an object of interest. Furthermore, the detection of the aerosol particles and characteristics, such as their generation and the size, is essential in climate study and monitoring exhaust gases along with their particulate matter and implementation of emission standards.
One barrier to the detection of aerosol particles having a diameter in the nanometer range is that they are difficult to be detected optically. A number of techniques exist for detecting aerosol particles having a size smaller than optically detectable, such as first charging the aerosol particle. The charged particles are then collected and the induced electric current is measured in order to detect the presence or the amount of the particles. Also, some detection techniques involve growing the aerosol particles by condensing a certain condensing fluid vapor on the aerosol particles before attempting detection. The most widely used measurement method for submicron aerosol particle size distributions is the electrical mobility-based method, such as through the use of a Scanning Mobility Particle Sizer (SMPS) device. This method and device first charges the aerosol particles to a known charge state with a unipolar or bipolar charger, classifies these charged aerosol particles according to their electrical mobility in an electric field with a differential mobility analyzer (DMA), and then measures aerosol particle concentrations of a specific electrical mobility with a detector. In order to invert the measured electrical mobility data to obtain aerosol particle size distribution, accurate knowledge of aerosol particle charge probability distribution is required. For submicron particles, the Fuchs charge probability model is widely accepted and used.
The electrical mobility-based method works well but it has one key limitation. The main challenge is the low differential mobility analyzer (DMA) throughput because of low charge probabilities of aerosol particles smaller than 100 nm (nanometer). The charge probabilities tend to decrease with decreasing particle size. For instance, the charge probabilities of single charged 22.1 nm and 10.7 nm particles are only about 9% and 4%, respectively. For sub-2.5 nm particles, charge probabilities are almost zero (less than 1%). The low charge probabilities reduce the monodisperse aerosol throughput of a DMA. As a result, the data quality of an SMPS (scanning mobility particle sizer) measurement in this size may be poor because of low counting statistics. The low charge probabilities also mean that a majority of the aerosols are wasted when analyzed with electrical mobility methods. For instance, if the charge probability of a particle of diameter dp is 1%, for this size particle, only 1% of the sample will be analyzed, and 99% of the sample will not be analyzed and get filtered out. Any method to enhance the charge probability of this size particle from 1% to 10%, would generate about 10 times more samples that could be analyzed by the electrical mobility-based method and thus achieve better data quality and less waste of working fluid and sample particles.
Therefore there is a need for improving charge probabilities for submicron nanometer aerosol particles.